An internal combustion engine generates power by burning a mixture of fuel and air in a combustion chamber. An intake valve is opened by a camshaft for the air or the mixture to enter the combustion chamber. An exhaust valve is opened by the camshaft after combustion to discharge for exhaust gas from the combustion chamber.
Operation of the intake valve and the exhaust valve is adjusted depending on an engine rotational speed (RPM) since adequate valve lift or opening/closing timing of the valves varies depending on the engine RPM.
A method of varying the opening/closing timing of the intake valve or the exhaust valve in accordance with a low speed or high engine RPM in order to supplement drawbacks of the general engine is called a variable valve timing (VVT) method.
An overhead camshaft, which is a hollow camshaft, comprises an outer shaft and an inner shaft rotatably inserted therein.
There are two kinds of cam lobes in the overhead camshaft; one kind of which are first cam lobes fixedly installed on the outer shaft, and the other kind of which are second cam lobes fixed to the inner shaft and rotatable on the outer shaft.
The overhead camshaft comprises two types of valve connected thereto; a first type of valve moves invariably in line with engine timing without special control, and movement of a second type of valve is controlled according to a phase of the valve to differentiate from the first type of valve.
A control apparatus varying a phase between a first cam lobe and a second cam lobe is called a cam phaser.
By using the overhead camshaft and the cam phaser, continuous variable valve timing (CVVT) method can be realized.
Positions of holes and slots must be accurately adjusted and fixed to obtain a coaxial structure between the outer shaft and the inner shaft for the overhead camshaft to be accurately controlled. Since the second cam lobe is fixed to the inner shaft by a pin for fixing the second cam lobe to the inner shaft, the pin is inserted through a fixing hole formed on one side of the second cam lobe, and a slot formed on one side of the outer shaft. A pin hole is formed through the inner shaft in order, continuing through an axis of rotation of the inner shaft and another slot on the opposite side of the outer shaft to another fixing hole on the opposite side of the second cam lobe.
Thus, an adequate apparatus in an assembly process is necessary to secure the mass production technology.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.